There are many requirements for having a particular waveform shape or pulse envelope of an amplitude modulated RF signal. Such a pulse is particularly advantageously used where, for example, an amplitude modulated pulse on an RF carrier signal is being detected, and where it is desired to provide narrow band operation on one or two closely spaced frequencies. This can occur for example in distance ranging systems. Interference in a range measurement provides an error whose magnitude often depends on the severity of the interference. The pulse shape and its filtering can often be chosen to minimize this interference. However, such ranging systems usually employ high frequency signals and fast response times that greatly limit the use of particularly shaped pulse envelopes that can be generated in a reasonable manner, with relatively small, simple and light weight equipment. Such shaped envelopes are normally generated by built up L/C networks that can be complex, heavy and expensive.
Further in such systems, it is often desirable to be able to easily increase the length of the pulse to make it distinguishable from other pulses on a single carrier frequency system. Again this has to be accomplished in a simple, quick and yet accurate manner.
So it is advantageous to have an improved method and apparatus for digitally controlling the amplitude modulation of a pulse envelope on an RF signal.